In the field of four-stroke gasoline engines, there have been proposals to use valve lift varying mechanisms with the aims of improving engine output and fuel economy and reducing undesired emission from the engine. It has been practiced to prepare low speed cams and high speed cams on a same camshaft and select the cams according to the operating condition of the engine. It has also been practiced to interpose a control arm or control link between a valve cam and a rocker arm and varying the geometry of the control arm or control link for varying the valve lift in a continuous manner (See WO2002/092972 and Japanese patent laid open publication No. 2005-248874). Presently, there is a growing demand for a system that can vary the cam phase and valve lift individually.
The inventors of the present application have developed a variable valve lift system for a multi-cylinder engine which uses a control shaft pivotally supported by a cylinder head so as to be able to move angularly around a rotational center line extending in parallel with the camshaft of the engine. The control shaft pivotally supports a control link having a free end interposed between the cam lobe and the rocker arm. This provides a favorable solution to the task of providing a compact and reliable variable valve lift system.
The inventors have also noted that a pivot arm that pivotally supports the control shaft is subjected to a significant load, and it is important to ensure a high mechanical rigidity in pivotally supporting the control arm so that the tilting or twisting of the control shaft may be avoided. It was also noted that lubrication of various parts is highly important for ensuring a reliability of the system.